This was done to avoid a recession which would have likely reduced GDP by 5% or so for a year. Not smart, but that's political decision making for you. Politicians always benefit when they spend more money, so they do.

Edit: There has been no year of >2% GDP decline since the end of WWII. The Great Depression saw an annual drop in GDP of 13.0% in real dollars.

Just to let you know what we're risking 50% of GDP for (some portion of which will actually be spent).